The present invention relates to a method for carrying out isomerization of glucose under expanded bed conditions.
Glucose syrup prepared by enzymatically liquefying and dextrinizing an aqueous (corn) starch suspension, the dextrin thereafter being enzymatically saccharified, may be enzymatically isomerized into a glucose-fructose mixture syrup by contacting the glucose syrup with a microorganism derived glucose isomerase preparation using reaction conditions such as pH temperature enzyme concentrations, contact time, etc. which achieve an optimum conversion to a glucose-fructose mixture reasonably approximating 50:50 glucose-fructose. High fructose syrups are sweeter than glucose syrups, and have been substituted widely for sucrose (i.e. cane and beet sugar syrup).
As the high fructose syrup art developed into a large scale industry workers in the art became interested in adopting long standing process design principles, including for example the possibilities of carrying out the isomerization of glucose syrups under fluidized bed conditions. U.S. Pat. No. 3,928,143 describes in some detail the desirability of carrying out enzyme catalyzed reactions with an expanded bed of enzyme catalyst particles and approximately plug flow for the fluid.
Glucose isomerase is normally an intracellular enzyme, and this enzyme as initially produced is simply a collected mass of microorganism cells. Processing the cells to liberate a pure enzyme then bonding such an enzyme to the dense particle required for the process described in U.S. Pat. No. 3,928,143 makes the enzyme coated dense particle relatively expensive. Manifestly conversion of the cell mass itself into fluidizable particles would offer substantial cost advantages.
An object of this invention is to provide a cell mass glucose isomerase preparation in fluidizable particle form.
A further object of this invention is to provide an expanded bed procedure for carrying out isomerization of glucose.
Conversion of the individual glucose isomerase containing microorganism cells into reusable relatively large particles has been accomplished by prior workers in the art, availability of such an enzyme form being a major prerequisite for fluidized bed isomerization. Reference is made to U.S. Pat. No. 3,821,086 and to pending U.S. application Ser. No. 501,292 filed Aug. 28, 1974, now U.S. Pat. No. 3,980,521 for the details of quite diverse methods for converting glucose isomerase microorganism cells into cell mass particulate form. The terms cell mass particles, and cell mass particulate form are intended to refer to particles formed or fabricated from the substance of the microorganism cells and organic reactants such as glutaraldehyde, proteins, or agglomerating agents e.g. polyelectrolytes.
However, a specific disadvantage of cell mass particles is their relatively low density. Necessarily the particles fall within the density range of biologically derived substances. For example the true density of enzyme particles made according to the preferred practice described in Ser. No. 501,292 is about 1.4g/ml. For expanded bed purposes such low density enzyme preparations constitute so significant a disadvantage as to raise doubt whether isomerization under expanded bed conditions is feasible with cell mass particulate form enzymes.
It has however, been determined that glucose isomerization can be carried out successfully under expanded bed conditions with cell mass particulate enzyme preparations.